The present invention relates to an apparatus and method for loosening a stuck section of a downhole drill string within a well borehole. More particularly, but not by way of limitation, the present invention relates to collapsing a subassembly along a section of a rotatable drill string to reduce the subassembly's outside diameter while at the same time initiating within the string a jarring action or force that resonates along the entire drill string and simultaneously allowing drilling fluid inside the drill string to circulate to the outside of the string within the well borehole. All of the structural features and actions of the present invention cooperate to collapse a sub-section of the drill string allowing upstream sections to continue to rotate within the borehole. The collapsing subassembly may be a drilling stablizer, a reamer, or even a casing scraper. In some applications, the collapsing subassembly need not be stuck to activate the natural jarring actions and the circulating features of the present invention.
A drill string is used to drill a subterranean well bore. The drill string typically consists of multiple joints of drill pipe, drill collars, and a drill bit. To facilitate completion of the well, it is important that deviation from vertical be controlled. In the past, deviation of the well bore has been controlled by the manipulation of the string weight on the drill bit or directional control tools, such as mud motors and monel collars. The length, weight, and outside diameter of the drill collars help maintain stabilization while applying a sufficient amount of weight on the bit to affect bit penetration. However, too much weight on the bit may result in hole deviation problems.
Additional equipment has been used to stabilize the drill string. These devices are commonly known as stabilizers. These tools have a larger outside diameter than the drill collars and are in constant rotational contact with the sidewall of the well bore during the drilling process. The problem with stabilizers is that the contact between the stabilizer and the well bore can be the source of many problems. For example, penetrated, soft formations may collapse or swell inwardly after penetration of the bit which may in turn cause the stabilizer to become stuck. In addition, water loss in some formations may cause excessive mud cake buildup on the wall of the well bore which can also cause sticking to occur.
There are times when other subassemblies other than stabilizers get stuck, slowing or stopping the drilling process. Sometimes reamers which are cutting a larger bore above the drill bit bore become lodged in the walls of the formation. Occasionally, a casing scraper used to clean an in place casing run also becomes stuck within the casing. These problems are tremendously costly to correct with current technology. Often the drill string must be left downhole and the well bore redrilled.
Further, if a subassembly does become stuck, this can lead to the drill string becoming stuck in several additional locations along the string if rotation of the drill string and circulation of drilling fluid is not maintained. The present invention allows the stuck subassembly to cease rotating while the sections above the stuck one continue to rotate. Further, it may be difficult to free the drill string from being stuck if the point of sticking is not known, and the process of determining the sticking point is expensive and time consuming.
To this end, a need exists for a subassembly that is capable of being selectively collapsed to reduce its outside diameter if the sub becomes stuck thereby possibly eliminating the point of sticking. A need further exists for a drill string that is capable of maintaining circulation and rotation above the point of sticking to prevent further sticking of the drill string. Further, there is a need to be able to jar the string internally when stuck, and to be able to locate where along the string the subassembly is stuck. It is to such an apparatus that the present invention is directed.